I'm not trying to answer your question with more questions; but, I can't tell from your posting if the engine seems to be running fine other than no power or if it is definitely running like s#^+. So, without more info it's awful hard to say. Is it idleing ok? Does it act like it's starving for fuel or running rich or does it act more like a tranny/rear end problem? Is it an automatic tranny and if it is, is the tranny filled with fluid, and does it look black or smell burned? Have you pulled the rear end cover off to look at the rear end?